'Should have told him' that angry little whisper echoes in the back of Dean's head. (It's been coming around more and more often, ever since…ever since…)
And maybe it was right. Maybe he should have told him.
'Too late now.' he thinks. 'Too late to tell a dead man anything.'
But maybe a little part of him refuses to believe that Cas is-Cas is-
'Gone.' that little whisper says maliciously. 'Gone gone gone.'
But it's true, because Cas is gone, and he's not coming back, and the memory of him, sightless eyes gazing to the Heaven that had betrayed him, blackened wings outlined on the ground- that memory is going to stay with Dean, even when he's old and everyone else has left him, too.
'Should have told him but you didn't and now he's dead, just like John, just like Mary, like Ellen and Jo and everyone else who gets involved in your fucked up little life.'
"Should'a told you, Cas." Dean says to the funeral pyre.
(Even if it's not really Castiel's body, Jimmy Novak deserved a proper hunter funeral, as well. Dean can pretend that it's really Cas that they're gathered around, but the truth is that Cas was gone-gone gone gone- the second that angel-blade pierced his heart, and it was all his fault.)
'All your fault, Dean-o. Should have said 'yes', maybe you could have saved him, maybe you'd have gotten your chance to tell him.'
"Too late now." Dean murmurs, watching the smoke spiral up to the sky, and for a moment, he swears he sees wings.